Hybrid piston pin

ABSTRACT

A light-weight, high-strength composite pin for use in pin-jointed reciprocating mechanisms and a method of preparation thereof is provided. Basically, the pin has a tubular metal sleeve and an interior fiber-reinforced resin core. At least 50% of the fibers in the core are continuous fibers which are oriented at a predetermined specific angle of orientation ranging, in general, from 0° to about ±25°. Indeed, in a preferred embodiment of the present invention, the fibers are cross-plied at an angle of orientation of from about 5° to about 12°.

This is a division of application Ser. No. 51,682, filed June 25, 1979,now U.S. Pat. No. 4,311,406.

FIELD OF THE INVENTION

This invention relates to pins for pin-jointed reciprocating mechanismsand more particularly to light-weight, fiber-reinforced piston pins.

BACKGROUND OF THE INVENTION

Light-weight, high-strength composite structures are being employed inan ever wider variety of applications, particularly where the benefitsto be gained by use of such materials clearly offset the generallyhigher costs associated with them. One area of increasing use ofcomposite materials is in automotive components where use oflight-weight, high-strength components can be translated into higherfuel efficiencies. Examples of such light-weight, high-strengthcomponents include leaf springs, stabilizer bars, body parts and thelike.

Another potential automotive application for light-weight, high-strengthcomposite structures is in pin-jointed reciprocating mechanisms such aspiston pins and the like. For example, approximately 50% of the forcesencountered by a reciprocating engine component is the result of thecomponent's own weight. Therefore, a reduction in weight leads to areduction in load; and, this allows a further reduction in weight andincreased efficiency.

New light-weight, high-strength pins for pin-jointed reciprocatingcomponents have potential utility in other areas as well. For example,where engine performance is of paramount concern, such as with racingvehicles, composite piston pins and the like can result in greater poweroutput for a given engine design. Even small engines used, for example,on chain saws and the like would be vastly improved by use oflight-weight, high-strength components. The physically debilitatingvibrations endured by the operator of such mechanisms can besignificantly reduced by use of lighter weight pins for such pin-jointedreciprocating components. Potentially, light-weight, high-strengthreciprocating pins for compressors can afford considerable economicoperating benefits.

Despite this myriad of potential uses for such light-weight, composite,reciprocating components, there has been very little progress in thearea of developing suitable reciprocating composite parts. With respectto piston pins as a specific example, the high temperatures and highrepetitive loading on such a part have inhibited the commercialdevelopment of light-weight, high-strength piston pins.

SUMMARY OF THE INVENTION

Briefly stated, the present invention contemplates a pin for use in apin-jointed mechanism, especially a piston pin for a reciprocatingengine, formed of a tubular metal sleeve surrounding a fiber-reinforcedresin core. In general, the fibers of the core are continuous fiberswhich are oriented substantially at an angle ranging from between about0° to about ±25° with respect to the longitudinal axis of the pin. In apreferred embodiment of the present invention, the continuous fibers inthe fiber-reinforced resin core are cross-plied at an angle ranging frombetween about 5° to about 12° with respect to the longitudinal axis ofthe pin.

In accordance with another aspect of the present invention, an improvedpin for use in a pin-jointed reciprocating mechanism is prepared byforming a fiber-reinforced core member having continuous fibers orientedat a predetermined angle of orientation generally between about 0° and±25° with respect to the longitudinal axis of the core member andinserting said core member into a metal tubular sleeve, the sleeve andcore being sized so as to provide for a snug fit of the core member inthe tubular sleeve; and, thereafter, heating the assembly at elevatedtemperatures and for times sufficient to post-cure the resin within thetubular metal sleeve.

These and other embodiments of the present invention will becomeapparent upon a further reading of the specification in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a piston pin constructed inaccordance with the present invention.

FIG. 2 is a longitudinal sectional view of the particularly preferredpiston pin constructed in accordance with the present invention.

FIG. 3 is an isometric drawing, partly in perspective and partly cutaway, illustrating a preferred method of preparing the core member ofthe invention.

FIG. 4 is yet another isometric drawing, partly in perspective andpartly cut away, illustrating the method of preparing a preferred pistonpin in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As indicated hereinabove, the present invention is directed toward acomposite pin for pin-jointed reciprocating mechanisms. Since aparticularly preferred application for the pin of this invention is as apiston pin for internal combustion engines, reference hereinafter willbe made specifically to a piston pin. It should be understood, however,that all matters set forth herein are to be interpreted in anillustrative and not a limiting sense.

Referring now to the drawings, it should be noted that like referencecharacters designate corresponding parts throughout the several drawingsand views.

The piston pin 10 of the present invention is formed from afiber-reinforced core member which may be a solid core member 11 (seeFIG. 1) but preferably is a tubular core member 12 (see FIG. 2). Thecore member (11 or 12) is fitted within a tubular metal sleeve 14.

The metal sleeve 14 may be formed by numerous metals and metal alloyssuch as steel, aluminum and titanium. Preferably the metal sleeve isformed from a steel tubing such as 4130 steel tubing which has been heattreated to an appropriate strength and Rockwell hardness. For example,where wear is not as significant as strength, the metal sleeve may beheated to an ultimate strength of 200,000 psi. If wear is moreimportant, then metal sleeve 14 is heated to a Rockwell hardness of C-55or C-56, for example. The extent of heat treatment obviously is a matterof choice depending upon the use to which the pin is being placed. Themethod of heat treating is well known in the art and is not a part ofthis invention.

The core member (11 or 12) of the piston pin 10 of the present inventionis formed from a fiber-reinforced resin material. In the practice of thepresent invention, the fibers are continuous fibers and are selectedfrom typical fiber-reinforcing materials such as boron, carbon,graphite, glass, polyaramids and mixtures thereof. Preferably, however,the fibers are selected from carbon and graphite fibers, and moreparticularly from carbon and graphite fibers having a Youngs modulus ofabout 32×10⁶ psi and a tensile strength of about 400,000 psi or greater.

As indicated herein, the continuous fibers are embedded in a resinmatrix. In general, any resin may be employed, such as thermoplastic andthermoset resins, although it is preferred that the resin matrix be athermosetting resin.

Suitable thermosetting resin materials include epoxy, polyimide andpolyester resins.

The epoxy resins are polyepoxides which are well known condensationproducts or compounds containing oxirane rings with compounds containinghydroxyl groups or active hydrogen atoms such as amines, acids andaldehydes. The most common epoxy resin compounds are those ofepichlorohydrin and bis-phenol and its homologs. The polyester resinsare polycondensation products of polybasic acids with polyhydricalcohols. Typical polyesters include polyterephthalates such aspolyethylene terephthalate. The polyimide resins are derived frompyromallitic dianhydride and aromatic diamines.

The amount of fiber in the resin will vary depending upon the choice offiber or fibers, the strength and weight characteristics of the ultimatepart and the like. In general, for an internal combustion engine pistonpin, from about 50 volume % to about 65 volume % and preferably from 60volume % to about 65 volume % of carbon fiber in the resin will beemployed. Particularly preferred is from 60 to 65 volume % of continuouscarbon or graphite fibers in an epoxy resin matrix.

As should be readily appreciated, randomly oriented staple lengths offiber filaments may also be included. In the event that randomlyoriented fibers are included, at least greater than half of the fibersin the fiber-reinforced resin matrix core member (11 or 12) will becontinuous specifically oriented fiber-reinforcing material.

The continuous fibers in the core member (11 or 12) of the piston pin ofthe present invention are oriented at a predetermined angle oforientation which ranges generally from about 0° to about ±25° withrespect to the longitudinal axis of the core. Indeed, it is particularlypreferred that the continuous fibers be oriented at an angle rangingfrom between about ±5° to about ±12° with respect to the longitudinalaxis of the core. As will be readily appreciated, the "±" designationindicates that the fibers are cross-plied; that is, for an angle oforientation say of ±10°, half the fibers are oriented at +10° and halfthe fibers are oriented at -10° with respect to the longitudinal axis ofthe core. This cross-ply orientation can be seen, for example, in FIGS.3 and 4.

In fabricating the piston pin of this invention, a core member (11 or12) is provided having the fibers 21 therein at the requisite angle oforientation with respect to the longitudinal axis of the piston pin. Forexample, when the fibers in the core member are to be oriented at 0°with respect to the longitudinal axis of the piston pin, the continuousfibers are passed through an appropriate resin mixture where the fibersare impregnated with an appropriate amount of resin and then through adie where the fibers and resin are consolidated and cured into acylindrically shaped core member having the fibers therein oriented at0° with respect to the longitudinal axis thereof. Optionally the resinbath through which the fibers are pulled may contain staple length fiberfilaments so that the resulting cylindrically shaped core member willhave randomly oriented fibers as well as continuous fibers oriented at0° with respect to the longitudinal axis thereof.

In the instance where the fibers in the core are cross-plied at apredetermined angle of orientation, such as in a particularly preferredembodiment of the present invention, the core is formed from a pluralityof sheets of resin impregnated, continuous, unidirectional fibers byfirst cutting the sheets in a predetermined flat pattern, generally inthe shape of a rectangle. Then the sheets are arranged, one on top ofthe other, in laminate form in a manner such that the fibers in eachadjacent layer are cross-plied with respect to each other. For example,as is shown in FIG. 3, the unidirectional fibers 21 in the variouslayers of sheet material 14, 15, 16 and 17 are oriented at a specificpredetermined angle with respect to the longitudinal axis of the sheetmaterial. In layers 14 and 16, the fibers 21 are oriented at a specificangle, θ₁, with respect to the longitudinal axis of the sheet material.In layers 15 and 17, the fibers are oriented at a specific angle, θ₂,with respect to the longitudinal axis. The magnitudes of θ₁ and θ₂ arethe same but of different directions. Since the various layers of sheetmaterial also are arranged in alternating sequence, the fibers inadjacent layers will be cross-plied with respect to each other. Theselayers of sheet material then are wound around a mandrel, such asmandrel 25. After so winding, the sheets are held in place on themandrel by cellulose tape or an appropriately shaped tool which serves,in effect, as a mold. Thereafter, the entire assembly is heated so as tocure the resin.

The temperature at which the assembly is heated for curing depends, ofcourse, on a number of factors, including the type of resin which isused to impregnate the fibers. These temperatures are well known.Typically for epoxy resin impregnated fibers the temperature will be inthe range of from about 100° C. to about 180° C. and preferably about180° C. Similarly, the time for heating will depend upon the curingtemperature employed for the particular resin used.

After curing, the assembly is removed from the mold, the mandrel isremoved, and the resultant core member is inserted in the tubular metalsleeve 14.

Since a number of plies or layers of fiber-reinforced sheet materialthat are employed in making up the core member 12 are used in amountssufficient to provide a core having a sufficiently large diameter toprovide a tight fit of the core within sleeve 14, it is sometimesnecessary to grind the exterior surface of the cylindrical core member12 so as to be able to fit the core within the sleeve 14 with therequisite snugness. Indeed, slight oversizing of the core followed bycenterless grinding is a very desirable method of assuring that the core12 will have the requisite dimensions for a snug fit within sleeve 14.

Optionally, prior to inserting the core (11 or 12) into sleeve 14, anadhesive can be applied to the inner surface of the sleeve 14, the outersurface of the core or both. Typically a thixotropic paste-type epoxyadhesive is used such as Hysol, EA 929 sold by the Hysol Division ofDexter Corporation, Pittsburgh, Calif.

After pressing the core into the metal tube 14, such as shown in FIG. 4,the assembly is then heated, for example, in an oven for post-curing andstress relief. Thus, the assembly is heated at temperatures in the rangeof about 125° C. to 175° C., and preferably at 150° C., for timesranging from about 12 to 20 hours and preferably 14 to 18 hours.

After the post-curing step, the assembly can be ground to provide achamfer and a uniform O.D. if such is necessary.

To further illustrate the present invention, reference is made herein tothe following examples.

EXAMPLE 1

Following the procedure outlined above, a piston pin for a small block,8 cylinder automotive engine was fabricated. The piston pin (sleeve andcore) had a length of 3.008 inches. The core 12 had an inside diameterof 0.5 inches and an outside diameter of between 0.8675 inches. Theouter diameter of sleeve 14 was 0.9271 to 0.9272 inches. The innerdiameter of sleeve 14 was sufficient to accommodate a snug fit of thecore 12 when pressed into the sleeve. Sleeve 14 was made from 4130 steelhaving a Rockwell hardness of C-56. A 45° chamfer was provided in eachend of sleeve 14. The core 12 was made from continuous carbon fiberreinforced epoxy resin. The angle of orientation of the continuouscarbon fibers was ±10°. The pin so formed was found to be 50% lighter inweight than the standard all metal piston pin. The pin was tested in aservo-hydraulic fatigue testing machine and at one million cycles thepin had not broken.

EXAMPLE 2

In this instance, a piston pin for a one cylinder racing motor wasfabricated as set forth above. The pin (core and sleeve) had a length of1.900 inches. The core 12 had an inside diameter of 0.125 inches and anouter diameter of 0.45 inches. The outside diameter of the sleeve 14 was0.49 inches. The core was pressed into the sleeve and held there snugly.Sleeve 14 had been heat treated to an ultimate strength of 200,000 psiand a Rockwell hardness of C-44. A 45° chamfer was provided in both endsof sleeve 14.

The core 12 was made from continuous carbon fibers in an epoxy matrix.The fiber orientation in the core was ±10°. The pin fabricated provideda weight saving of 33%. The pin was field tested in the racing vehiclefor over one million cycles without failure.

What is claimed is:
 1. A method of making a pin for a pin-jointedreciprocating mechanism comprising:forming a fiber-reinforced resin coremember having at least 50% of continuous fibers therein, said fibersbeing oriented at a predetermined angle of orientation of between about0° to about ±25° with respect to the longitudinal axis of said core;inserting said core in a tubular metal sleeve, said sleeve and corebeing of predetermined dimensions to provide a prestressed, snug fit ofsaid core in said sleeve; heating said core and sleeve at elevatedtemperatures and for a time sufficient to post-cure said resin of saidcore and to relieve said stress of said snug fit.
 2. The method of claim1 wherein said heating is at temperatures in the range of from about125° C. to about 175° C. for about 12 to about 20 hours.
 3. A method ofmaking a pin for a pin-jointed reciprocating mechanismcomprising:providing a plurality of sheets of resin impregnatedunidirectional continuous fibers in the form of a predetermined flatpattern, said fibers being oriented at a predetermined angle oforientation with respect to the longitudinal axis of said flat pattern,said angle being in the range of from about 0° up to about 25°;arranging said sheets in alternating fashion one on top of the next toprovide a laminate whereby the fibers in adjacent sheets are cross-piledwhen said angle is greater than 0° and whereby said fibers in adjacentsheets are unidirectional when said angle is 0°; wrapping said laminatearound a mandrel; heating said assembly to cure said resin; allowingsaid assembly to cool to ambient temperatures; removing said mandrel;providing a tubular metal sleeve; inserting said fiber-reinforced curedresin into said tubular sleeve to form a prestressed snug fit betweensaid cured resin and said tubular sleeve; heating said sleeve andfiber-reinforced resin to post-cure said assembly and to relieve saidstress of said snug fit.
 4. The method of claim 3 wherein said fibersare selected from the group consisting of carbon, boron, graphite,glass, polyaramides and mixtures thereof.
 5. The method of claim 4wherein said assembly is heated from about 100° C. to about 180° C. fora time sufficient to cure said resin.
 6. The method of claim 5 whereinsaid metal of said sleeve is steel.
 7. The method of claim 6 whereinsaid sleeve and resin core are heated in the range of from about 125° C.to about 175° C. for about 12 to about 20 hours.